Measuring the intensity of ultraviolet rays



Feb. 16, 1932. w. FRANKENBURGER ETAL 1845835 MEASURING THE INTENSI'I'Y OF ULTRAVIOLET RAYS Filed June 5. 1928 Patented Feb. 16, 1932 UNITED STATES PATENT OFFICE WALTER IRANXEI'B'UBGEIB, 01' LUDWIGSEAIIZN-ON-THE-RHIN'E, RUDOLF ROBL, O'.F IANNHEIH, AIVD WILHELI ZIIHERHAIN'N', OII' I'BIEDRICHSIII'ELD, GEIBZNIANY, ABSIGNORS T I. G. I'ARBENINLDUS'IRIE AI'.IIIENGESELLSCXAFT, 01' FRANKFORT- 0N'4IEHIB-IAIII', GEBMANY, .A CORPOBATIGN 0! GERIANY IIASUIBING TBE IN'IENSI'I'Y 01' ULTRAVIOLET RAYS Applicatlon fled Iune 5, 1928, Serie] 1Ib. 283,130, and in Germany June 9, 1927.

Continuous checking of the radiaton intensity of the usual sources of light in the physiologically active region of ultra-violet radiation between 250, and 380, 1s

a. matter of considerable importance, especially in the case of mercury vapor c 1uartz amps, in view of the inconstancy. It 1s also frequently desirable t0 determine the proportion of ultra-violet rays in the dayhghtnn various localities, and the extent to wh 1ch this proportion suers diminution on passmg through windows and the like.

It is already known that certain socall ed phototropic substances undergo character1stic changes of 00101 when irrad1ated w1th visible 01 ultra-violet li ht, reversion ocearrng more or less rapid y when the irrad1atien is interrupted. This property of such substances is not in itself suflcient to enable rapid and simple measurements to be made of the intensity of radiation, since the phototrcpic substances a1ways tend to assume the maximum depth of shade irrespect1ye of the intensity of the ultra-violet radiat1on com 2 ing nto action.

We have now found that the intensty of radiation may be measured in a simple manner in the region of the ultraviolet rays, by making use of the color change of phototrepic coloring matters whch have a range of sensitiveness practicaly identical w1th the spectral area under examination, sultably determined amounts of substances being added which counteract the photochemical color change, and thus enable reproducible de grees of coloration te be obtained. These cclorations attain, after a short eriod of irradiation, a fina1 va1ue correspondmg to the intensity of radiation in action, which value can be numerically expressed in terms of color, preferably with the aid of color scales which are fast to light.

On the basis of precise spectrographie determinations, it has been fonnd that the S0111- tions of phototropic basic coloring mat-ters, such as the leucocyanides, carbinols or sulfurous compounds of coloring matters of the triphenylmethane series, come primarily under consideration as phototropie substances fo r ultra-violet light. These S0111- tions remain colorless in the visible and in the shortwave ultra-violet region of the spectrums but acquire intensive coloration on irradiation with ultra-vielet rays in the region between 210 an 350,.1L. This photochemical change is due to ionization of the phototropic coloring matter giving rise to strongly.colored ions. After exposure to the ultra-vielet ra.ys the colored ions disappear slowly, the leucwcyanides, carbinols or sulfur0us compounds of the coloring matters being re-formed. By the addition of substances furnishing an equal ion to those pres ent in the co1ored solution, such as for example potassium cyanide, caustic potash solution 01 sulfur0us acid the re-formation of the colorless compounds from the strongly colored ions is largely accelerated. Since the re-formation takes place also during irradiatien, an equilibrium between the ionization and the re-formation is established. The greater the intensity of the aetive rays the higher is the speed of the ionization while the speed of the re-formation remains unaltered and accordingly the coloration obtained corresponds to the amount of active irradiation. In the accompanying drawing the full line indicates the amount of colored ions present in a certain solution in the absence of additional substances. The dotted lines indicate the amount of colored ions present in the presence of the additional substances used according to the present invention, curve 1 indicating the amount in the case of strong irradiation and curve 2 that in the case of weak irradiation.

The numerical determination of the degree of coloration attained, and thereby of the radiation intensity under examination is preferably efiected colorimetrically, by comparing the color of the irradiated specimen after equlibrium has been reached with a correspondingly graded c0lor scale. The best method of eflecting the comparison is by preparing solutions of the coloring matter formed by irradiation in a non-phototropie form, and using this for the comparison. Thus, for instance, when employing the leucocyanide of a basic coloring matter for meas uring the -radiation intensty, from which on irradiation with ultra-violet rays the coloring matter itself is re roduced, the color scale is made from gra ually diluted solutions of the coloring matter itself. The scale nay be graduated, by means of a series of preliminary comparative tests only once perfornied, in customary units of measurement, for example units of energy of the radiation per square centimetre, or sometimes in units which correspond to the physiological act1on of the radiation, such as the production of erythema on the skin. By means of the sa1d solutions and addition it is easy to measure the radiation intensity of the medicinally important ultra-violet region of artificial sources of light, such as mercury vapor quartz lamps, as well as the content of ultraviolet rays in the sun rays at different alt1- tudes of the atmosphere.

The above described process of measuring the intensity of radiation of sources of ultraviolet rays allows of a simple and precise manner of determining the amount of irradiation with ultra-violet rays to be applied.

The following examples will further illustrate the nature of the said inventon which however is not limited thereto. The

parts are by weight.

Emample 1 1 parts of a cold-saturated solution of potassium cyanide in ethyl alcohol are added to 100 parts of a cold-saturated solution of crystal violet leucocyanide in ethyl alcohol. The colorless solution is placed in a quartz tube and is exposed, at varying distances, for at least 1 minute, to the light of a mercuryvapor quartz lamp. According to the distance from the lamp, a varying depth of coloration is produced, the degree of which can be ascertained by means of a color scale. This latter may be prepared in the following manner, namely by dissolving 0.02 gram of crystal violet in 100 cc. of absolute alcohol, and dluting 10 cc. of this solution with 10.6 cc. of absolute alcohol, the mixture being well shaken. Of this solution in turn, 10 cc. are diluted with 10.6 cc. of absolute alcohol and so on until 10 dilutions are prepared, forming the 10 degrees of the color scale.

Proceeding on these lines, a source of light of the mereury-vapor quartz lamp type gives the following valuesz Distance Degrees on trom lamp the scale (4 100 om. 5 Ewample 2 6 parts of a cold-saturated solution of potassium cyanide in ethyl alcohol are added to 100 parts of a cold-saturated solution of fuchsine leucocyanide in ethyl alcohol. The

colorless solution be exposed to sunlight, in

a quartz tube, a red coloration is produced in from 1 to 2 minutes, the depth of which does not increase on prolonging the exposure compared with a standard solution of fuchsine. The coloration obtained in diffuse daylight is considerably weaker, and no coloration at al] is produced by the light of an incandescent electric lamp. On being placed in the dark, the colored solutiondecolorizes in about 20 minutes. In this manner, it is possible to measure the proportion of ultraviolet radiation in any source of light. A solution suitable for measuring the intensity of sources of ultra-violet light can also be prepared by adding an accurately calculated quantity of caustic potash solution to a solution of the carbinol base of fuchsine or of any other triphenylmethane dyestu.

Emample 3 Sulfur dioxid is passed into an aqueous solution of 1 gram of malachite green in 200 cc. of water, until complete decoloration occurs. The colorless solution is heated on the boiling waterbath, to eliminate the surplus sulfur dioxid. As soon as the color turns dark green, the solution is cooled, thereby again completely losing its color. A solution prepared in this marmer contains exactly the excess of sulforous acid needed for establishing a state of equilibriurn during irradiation.

What we claim is 1. A process of measuring the intensity of radiation of sources of ultra-violet rays which comprises exposing to irradiation a solution of a compound selected from the group consisting of leucocyanides, carbinols and sulfurous compounds of a basic coloring matter, to which such small amounts of an agent furnishing an ion equal to that formed by ionization of the phototrophic coloring matter as do not entirely prevent the change of color have been added, and determining the degree of color change by comparison with a scale of standard solutions of a coloring matter.

2. A process of measuring the intensity of radiation of sou:ces of ultra-violet rays which comprises exposing to irradiation asolution of a compound selected from the group consisting of leucocyanides, carbinols and sulfurous compounds of a coloring matter of the triphenylmethane series, to wh1ch such small amounts of an agent furnishing an ion equal to that formed by ionization of the phototrophic Coloring matter as do not entirely prevent the change of color have been added, and determining the degree of color change by comparison with a scale of standard solutions of the coloring matter formed by irraclation.

3. A solution for measuring the intensity of radiation of sources of ultrwviolet rays comprising a phototrophic coloring matter selected from the group consisting of leuco cyanides, carbinols and sulfurous compounds of a basic coloring matter, and an agent capab1e 0f furnishing an ion equal to that formed by ionization of the phototropic coloring matter in an amount insuflicient to entirely prevent the change of 00101 of said phototropic coloring matter on exposure to ultraviolet rays.

4. A solution for measuring the ntensity of radiaton of s0urces of ultra-violet rays comprising a phototropic coloring matter selected from the group consisting of leucocyanides, carbinols and sulfurous com ounds of color ing matters of. the tripheny ethane series, and an agent capable of furnishing an ion equal to that formed by ionization of the phototropc coloring matter in an amount in suflicient to entirely prevent the change of color of said phototropic coloring matter on exposure to ultraviolet rays.

In testimony whereof we have hereunto set 0111 hands.

WALTER FRANKENBURGER. RUDOLF BOBL. WILHELM ZIMMERMANN. 

